Some scientists think new types of bird flus should arise only in chickens, not in labs. Here a worker collects poultry on a farm in Kathmandu, Nepal, where the H5N1 virus was infecting animals in October 2011.
Prakas Mathema/AFP/Getty Images
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A vendor weighs a live chicken at the Kowloon City Market in Hong Kong last April. After closing live poultry shops in many cities around China, the rate of new H7N9 infections sharply declined.
Lam Yik Fei/Getty Images
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A woman wearing a mask rides past a KFC restaurant in Shanghai last month. Food scares and the bird flu haven't stopped many chicken lovers in the city from visiting KFC and other restaurants.
Aly Song/Reuters /Landov
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A health worker collects pigeons from a trap at People's Square in Shanghai, China, earlier this month. So far, workers have tested more than 48,000 animals for the H7N9 flu virus.
ChinaFotoPress/Getty Images
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With Bird Flu, 'Right Now, Anything Is Possible'

A vendor weighs a live chicken at the Kowloon City Market in Hong Kong Friday. Health authorities there have stepped up the testing of live poultry from China to include a rapid test for the H7N9 bird virus.
Lam Yik Fei/Getty Images
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